JPH0879887A - Method for extension of flat characteristic range of low sound and mechanical damping in speaker system for electroacoustic transducing - Google Patents

Abstract

PURPOSE: To extend a reproduction limit of a low sound frequency, to make a sound pressure characteristic flat and to strengthen mechanical damping by applying an electromotive force induced in a 2nd voice coil of a main speaker to a voice coil of a sub-speaker. CONSTITUTION: The system is made up of a dynamic direct-radiation main speaker A of a so-called double voice coil system having two voice coils L1, L2, a closed cabinet surrounding the speaker A, a dynamic direct radiation sub speaker B arranged to a rear side or a side face of the cabinet C, and an closed or partly open cabinet D surrounding the speaker B. Two voice coils L1, L2 are wound onto the main speaker A and the lap winding or a little distant apart parallel winding is adopted for the winding of the coils L1, L2. The 2nd voice coil L2 of the main speaker A is connected to the voice coil M of the sub speaker B with the same polarity. A low-pass filter is inserted to a connection line depending on the characteristic of the 2nd voice coil L2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expansion of the bass reproduction limit, flattening of its sound pressure characteristics, and enhancement of mechanical braking for an electro-acoustic conversion speaker system in a high fidelity audio reproduction device. It is about the method.

[0002]

2. Description of the Related Art An electro-acoustic transducer in a high fidelity audio reproduction device, so-called high-fidelity audio equipment
A speaker system in which a so-called cone type speaker of an electrodynamic type and a direct radiation type is used and a back surface of the speaker is surrounded by a cabinet is often used. Especially from 20Hz to several 100H
In the bass range up to z, this cone type speaker system with an enclosure is adopted as almost the only electro-acoustic transducer.

The bass reproduction limit of this system is defined by the mechanical resonance frequency Fco between the mass of the moving part of the speaker and the air elasticity in the cabinet, and the increase ratio of Fco to the natural resonance frequency Fo of the speaker is the aperture and the cabinet contents. It depends on the product. The radiated sound pressure response in the low frequency range below Fco drops sharply.

Further, since the driving point impedance near the resonance frequency Fco increases in a mountainous manner, when the output impedance of the power amplifier to be driven is large, a large mountainous swell also occurs in the sound pressure response, and the bass range is low. Hurt your hearing.

In order to keep Fco low, it is ideal to increase the internal volume of the cabinet. However, there are some restrictions due to the circumstances of actual installation. There is also a method of using a speaker having a small caliber after making the natural resonance frequency as low as possible. However, if the caliber is made smaller, the vibration amplitude required to obtain the same sound power increases, which causes a side effect of increasing distortion. Further, in order to suppress the natural resonance frequency of the speaker having a small diameter to a low value, it is necessary to increase the mass of the vibrating part, so that the conversion efficiency to the acoustic power also decreases.

With the intention of improving the bass response below Fco, a so-called bass reflex box system is widely used in which an appropriate duct is provided in the front of the cabinet and the resonance of this portion is utilized to extend the bass reproduction limit. However, there is a problem in that the swell of the sound pressure response is accompanied, and the dullness of the rising response due to the use of resonance is caused.

A technique called a symmetric drive system is one that has been subjected to the technique of more actively reducing Fco. The sound pressure in the cabinet surrounding the main speaker is absorbed by the sub-speakers installed in the back of this cabinet and driven in parallel, increasing the air compliance in the cabinet and ideally equivalent to an infinite enclosure. It is something to put.

[0008] The back side of the sub speaker itself must be surrounded by a cabinet that keeps a sufficient volume, and the mechanical resonance of this part becomes a problem. This is to be kept sufficiently low by reducing the aperture of the sub speaker. Is. However, it does not have active braking measures.

[0009]

[Problems to be Solved by the Invention] Direct emission type speaker
One of the important problems of the system is to lower the frequency of Fco, and the other is to suppress the increase of sound pressure response due to the increase of impedance in Fco.

A characteristic common to all the direct emission type speaker systems seen above is that the counter electromotive force of the voice coil can be absorbed to dampen the inertial motion of the cone in order to suppress the increase in sound pressure response at Fco. That is, it is premised on driving by a power amplifier having a low output impedance. That is, the damping of the driving power amplifier
It requires a large factor. Otherwise,
An excessive increase in the sound pressure response around Fco is unavoidable, which causes a harmful effect on hearing.

However, the power amplification element in recent years is generally a current amplification device, and the output impedance of the power amplifier constructed by this is inevitably very large as it is. Therefore, in the present situation, a large amount of negative feedback such as an emitter-follower output circuit and a positive overall NFB is performed to suppress the apparent output impedance.

However, a large amount of negative feedback has been pointed out as a problem such as instability of transient characteristics of an amplifier, and has been regarded as a problem in a field requiring high fidelity. In addition, a power amplifier with negative feedback must secure a wide dynamic range, and in the end, the effective power efficiency will decrease at an accelerated rate in response to the amount of negative feedback, and the power amplifier will have an unnecessary large amount. The result is the promotion of electrification.

The conventional symmetric drive system designed to actively lower Fco does not take into consideration the impedance rise itself in Fco. In addition to the resonance moved to the low range, the damping against the new mechanical resonance that appears due to the complicated arrangement is not internally taken, and the impedance and sound pressure characteristics are flattened by the driving electric device. ing. That is, it is premised on low impedance driving.
Therefore, the above-mentioned drawbacks are not solved.

Further, since the role of the sub-speaker in this system is to absorb the sound pressure near Fco, it is not necessary to operate in a frequency band higher than that and it is also a harmful effect. Therefore, a low-pass filter is built in. It is customary to drive the sub-speaker with a separate independent power amplifier.
Therefore, the load on the power amplifier side becomes large.

When the independent power amplifier on the side of the sub-speaker is omitted and both the main and sub-speakers are driven in parallel by a single amplifier, an unnecessary reduction in power efficiency is caused in a frequency band other than Fco. . To avoid this, the method of inserting a low-pass filter in the sub-speaker connection line is F
Since co is generally at an extremely low frequency, the inductance element has a heavy load and is difficult.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to relatively easily expand the reproduction limit in the low sound range without increasing the load on the driving device side such as a power amplifier.

At the same time, an excessive vibration near the resonance frequency is damped inside the speaker system to suppress an increase in impedance, so that the sound pressure response is flattened without depending on the characteristics of the driving device.

In this way, it is possible to allow driving by a power amplifier with a small output which is simple and has no negative feedback, and it is possible to reproduce a more natural and high-quality high-fidelity voice.

[0019]

[Means for Solving the Problems] The means for solving the problems of claim 1 will be described with reference to the drawings. FIG. 1 is a block diagram.

A so-called double voice coil type electrodynamic direct radiation type main speaker (A) having two voice coils, a closed cabinet (C) surrounding the main speaker (A), and a rear or side surface of the cabinet. It is composed of an electrodynamic type / direct emission type / sub-speaker (B) and a closed or partially open cabinet (D) surrounding the sub-speaker.

The main speaker A has two voice coils (L
1, L2) is wound. As a method of winding both the L1 and L2 coils, there may be methods such as overlapping winding as shown in FIG. 2 and parallel winding with a small distance as shown in FIG. Let L1 be a first voice coil driven by a power amplifier and L2 be a second voice coil.

The first cabinet C surrounding the main speaker A is always of a closed type, but a relatively small capacity is acceptable.

As the sub-speaker B, a sub-speaker whose natural resonance frequency is kept as low as possible is selected, and generally, the diameter is made smaller than that of the main speaker, and the resonance frequency with the cabinet D is made low even if the volume is not so large. Design to be able.

The second cabinet D prevents the back pressure of the sub-speaker from sneaking into the front surface. However, the mechanical resonance created by the cabinet and the sub-speaker affects the reproduction range limit of the entire system, so that the cabinet C is usually used. Take a larger internal volume. The second cabinet does not have to be a completely closed box, but may have appropriate openings to disperse the resonance.

The second voice coil L2 of the main speaker is connected to the voice coil (M) of the sub speaker with the same polarity. Depending on the characteristics of L2, a low-pass filter is inserted in the connection line as shown in FIG. Since the cutoff frequency of this filter has a frequency characteristic in which the electromotive force of L2 is appropriate for high-frequency attenuation, as will be described later, it may be relatively high and can be simple.

Two voice coils (M1,
A double voice coil type speaker in which M2) is wound may be used. As shown in FIG. 5, M1 is connected to the voice coil L2 of the main speaker, and M2 is used as a detection coil of a motional voltage proportional to the piston movement of the speaker to be used as a feedback control signal or to further improve the characteristics. It can be used as a dynamically driven voice coil.

[0027]

When the first voice coil L1 of the main speaker A is current driven by an amplifier having a high output impedance, an electromotive force proportional to the piston movement speed of the cone is generated in the second voice coil L2. This voltage Vm has a peak frequency at the resonance frequency Fco created by the main speaker and the first cabinet C, and has a mountainous frequency response characteristic that attenuates before and after the resonance frequency Fco.

If the two voice coils L1 and L2 have the same number of turns, Vm at Fco is equal to the driving point voltage across L1 and the phases are completely matched.

When this Vm is applied to the sub speaker B, the sound pressure fluctuation in the first cabinet C is canceled by the complementary vibrations of the two speakers, as long as the electric conversion efficiencies of the main speaker and the sub speaker are similar. It is equivalent to having a very large compliance. Therefore, the resonance frequency between the first speaker and this cabinet can be dramatically reduced.

At the same time, the counter electromotive force Vm, which is a manifestation of dynamic energy caused by the inertial motion of the movable portion of the main speaker A, is transmitted to the second cabinet D via the sub speaker and converted into acoustic energy there. It Therefore, if appropriate acoustic damping such as a sound absorbing material is applied and energy scattering at this portion is effectively performed, a strong damping action on the vibration of A can be exhibited. As a result, the impedance increase in Fco is eliminated,
It leads to a very flat sound pressure characteristic.

The fact that the electromotive force Vm has a rapid damping characteristic on the high frequency side of Fco constitutes an ideal condition for concentrating the above-mentioned braking action on the periphery of Fco, which is most needed. Therefore, no special device is required on the side of the amplifier, no special circuit is required for the connection line between the positive and secondary speakers, or a simple low-pass filter is inserted.

In general, under the drive of a current output amplifier having a high output impedance, the load on the electric device side is not burdened, the sound pressure conversion characteristics are flat over a wide range, and the bass reproduction range is extended. A speaker system for electric-acoustic conversion can be constructed.

[0033]

EXAMPLES Examples will be described with reference to the drawings.
FIG. 6 shows an example of a direct radiation type speaker system which realizes the invention of claim 1. It is a system exclusively for low-frequency reproduction up to 1 kHz.

A cone-type woofer with a diameter of 30 cm is used for the main speaker A, and a cone-type woofer with a diameter of 20 cm is used for the sub-speaker B. Two voice coils L of A
1 and L2 have a lap winding structure, and both have a rated impedance of 8 ohms. B is a normal single voice coil (M). This also has a rated impedance of 8 ohms.

The internal volume of the first cabinet is 75 liters, and the internal volume of the second cabinet is 120 liters. Both have a closed structure and are made of 21 mm thick plywood. The sub-speaker B is arranged at a right angle to the main speaker for the sake of simplicity, but this is also sufficient.

L1 is connected to the connection terminal with the power amplifier, and L2 and M are connected with each other through the open / close switch (S). No special filter is provided.

[0037]

The flattening of the radiation sound pressure characteristic and the expanding effect of the low frequency limit brought about by the present invention are shown below by the actual numerical values of the above-mentioned embodiment.

First, the characteristics in the state where the technique according to the invention is not applied will be shown. FIG. 7 shows the drive terminal voltage when the main speaker A alone is driven by the high impedance output amplifier in a state where the partition plate between the sub speaker B and the cabinets C and D is removed in the speaker system of the embodiment. It is an amplitude frequency characteristic. Although the impedance characteristic of A is shown as it is, a large swell is seen near Fco of 40 Hz.

FIG. 8 shows the frequency characteristics of the radiated sound pressure in the same state. After all, a big excitement can be seen near Fco.

FIG. 9 shows the amplitude frequency characteristics of the L1 terminal voltage when driven by a high impedance output amplifier in the same state as the speaker system of the embodiment. As compared with FIG. 7, the bass range characteristic is significantly flattened.

FIG. 10 shows the frequency characteristics of the radiated sound pressure in the same state. Again, it can be seen that the sound pressure is dramatically flattened as compared with FIG. 8, and the response fall in the low range near the reproduction limit is alleviated accordingly. As a result, a large expansion of the bass reproduction range has been realized.

As described above, by adopting the speaker system according to the present invention, it is possible to extend the reproduction limit in the low frequency range without increasing the load on the driving device side such as the power amplifier, and to increase the resonance frequency in the vicinity of the resonance frequency. Vibration speaker
It can brake inside the system and realize a flat sound pressure response.

As a result, it is possible to drive with a simple and small output power amplifier without negative feedback, and it is possible to realize more natural and high-quality sound reproduction with high fidelity. .

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of claim 1.

FIG. 2 is a cross-sectional view of a double voice coil unit in which two voice coils are wound in a layered manner.

FIG. 3 is a cross-sectional view of a double voice coil unit in which two voice coils are wound in parallel.

FIG. 4 is a system configuration diagram in which a low-pass filter is inserted in the connection lines of the primary and secondary speakers.

FIG. 5 is a system configuration diagram in which a sub voice speaker of a double voice coil system is used.

FIG. 6 is an example of the present invention.

FIG. 7 is a frequency characteristic of a driving voltage of a speaker system without the technique of the present invention.

FIG. 8 is a frequency characteristic of radiated sound pressure of a speaker system that does not apply the technique of the present invention.

FIG. 9 is a frequency characteristic of drive voltage of the speaker system of the embodiment.

FIG. 10 is a frequency characteristic of radiated sound pressure of the speaker system of the example.

[Explanation of symbols]

 A primary speaker B secondary speaker C first cabinet D second cabinet F low-pass filter L1 primary speaker first voice coil L2 primary speaker second voice coil M secondary speaker voice coil M1 secondary speaker first voice coil M2 secondary Second voice coil of speaker S Open / close switch 1 Driving terminal 2 Feedback terminal

Claims (1)

[Claims] 1. A so-called double voice coil type electrokinetic system in which a first voice coil (L1) to be driven by a power amplifier and another second voice coil (L2) are separately wound or wound in parallel. Type main speaker (A)
A closed cabinet (C) surrounding the cabinet, an electrodynamic sub-speaker (B) installed on the back or side of the cabinet, and a closed or partially open cabinet (D) surrounding the cabinet. The electromotive force of the second voice coil L2 of the speaker is directly
A speaker system in which the compliance of the closed cabinet C is increased by adding the voice coil (M, M1) of the sub-speaker via the filter circuit (F), and at the same time, the braking action on the main speaker is enhanced.